For northern spotted owls, habitat loss still matters

As barred owls (Strix varia) have moved in and taken over threatened northern spotted owl (Strix occidentalis caurina) territory on the West Coast, management has focused mostly on removing barred owls.

But researchers wanted to see how much of northern spotted owl declines can be attributed to barred owl invasions and how much is due to habitat loss.

“In the ‘90s, barred owls were fairly rare, and management focused on habitat,” said Charles Yackulic, a research statistician with the U.S. Geological Survey and the lead author of a study published in Ecological Applications. “In the last decade, barred owls really increased, and in the early 2000s, people began to recognize them as a huge threat. There was a shift where people now talk almost exclusively about competition with barred owls and less about habitat. We want to remind people that both things matter.”

In the study, Yackulic and his colleagues analyzed the importance of habitat conditions and barred owl competition on northern spotted owl population dynamics in 11 study areas, in Washington, Oregon and California, and forecasted future scenarios with barred owl removal and changes in habitat. 

The researchers found that most recent northern spotted owl occupancy declines in large ranges are a result of barred owl competition. “For a few of the sites particularly ones in the north, things looked pretty bleak in the short term,” Yackulic said, including one site where spotted owls may disappear altogether in the next decade or two.  But for many sites, he said, it may be 30 to 70 years before their situation becomes dire.

While barred owl competition may be the biggest factor affecting them, Yackulic and his colleagues also found that habitat changes, including logging and fire management, play an important role in northern spotted owls’ long-term recovery.

In the short term, barred owls may need to be removed to sustain spotted owl populations, he said, but in the long term, managers need “to stay the course of habitat recovery — and to a greater extent if possible,” he said. Eventually, he said, that could lessen the need for barred owl removal.